Process of flowing filamentis in laminar flow surrounded by an outer area of turbulent flow



Oct. 4, 1960 c. BOYER 2,955,017

PROCESS OF mowmc FILAMENTS IN LAMINAR FLOW SURROUNDED BY AN. OUTER AREAOF TURBULENT FLOW Filed Aug. 4, 1958 v 2 Sheets-Sheet 1 INVENTORCLARENCE BOYER BY ya;

C. BOYER ENTS IN LAMINAR FLOW SURROU Oct. 4, 1960 2,9550] 7 NDED BYPROCESS OF FLOWING FILAM AN OUTER AREA OF TURBULENT FLOW 2 Sheets-Sheet2 Filed Aug. 4, 1958 Ely-'2 ATTORNEY Clarence Boyer, Swarthmore, Pa.,assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., acorporation-of Delaware Filed Apr. 4, 1958, Ser. No. 726,542

3 Claims. (Cl. 18-54) The present invention relates to a novel anduseful process for forming a filamentary structure. More particularly,it relates to an improved process for preparing fibers, filaments,ribbons, and the like at relatively high speeds. 7

One of the major problems in preparing filamentary structures by thevarious prior art processes is the fragility of the freshly formedthread line. Since the filament is fragile in the initial spinningstage, the filament may be easily damaged and various precautions arenecessary if good quality filaments are to be obtained. This has been aserious problem in the various wet-spinning procedures in Which apolymer solution is extruded into a coagulating liquid to formfilaments. Typical examples of such conventional processes are thepreparation of rayon filaments by extruding viscose into a coagulatingbath, the preparation of rubber filaments by extruding rubber latex intoa coagulant, and the preparation of filaments of condensation elastomersby extruding solutions of the elastomers into aqueous coagulating baths.It also represents a serious problem in the so-called matrix ordispersion type of spinning process. of a relatively cheapmatrix-forming material, such as sodium alginate, is added to a polymerin dispersion form.

The modified dispersion is then extruded into a setting medium for thematrix-forming material so as to form a fragile shaped articlecomprising a gel matrix containing immobilized discrete polymerparticles. The polymer particles in the gel structure are then coalescedor fused with a coalescing solution, into filaments, fibers, etc.,composed predominantly of the polymeric material but usually.

' tional viscose process, i.e., about 100 yards per minute,

it is clear that this procedure is notas attractive as it could be froma commercial standpoint. Even in those processes in which commercialspeeds are obtainable, such as in the viscose process, variations orfluctuations in the bath flow direction or velocity cause filaments ofpoor quality to be formed.

The seriousness of this problem is reflected in'the large number ofpatents which have issued describing techniques and devices forminimizing this problem. Many patents have suggested the use of spinningtubes to confine the bath liquid and to minimize turbulence in the bathflow. In many instances it has been recommended that the bath flow atthe same rate that the thread line is moving so that no appreciabletension will be exerted on the filament during the initial stages offormation. The use of counter-current flow or bath flowing more rapidlythan In this process a small amount- Patel 111:0

the thread line has also been suggested to provide some stretchingaction in the bath. In such cases, however, a smooth bore tube ofuniform cross section is always used.

It is an object of the present invention, therefore, to provide animproved spinning process which permits a substantial increase inspinning speeds with no damage to the filament. Another object is toprovide a process which improves liquid contact withthe filament,reduces the load on the filament, allows easier stringing up and permitsincreasing the speed of the process. A still further object is toprovide a process in which a freshly formed thread line is intimatelycontacted with a filamentforming liquid while being partially supportedby this liquid. Other objects will become apparent from thedescriptions, drawings, and the claims.

These objects are accomplished by the present invention which providesan improvement in the process of forming a filamentary structure bycontacting a freshly extruded polymer with a filament-forming liquid toform a filamentary structure; the improvement which comprises flowingthe filament-forming liquid concurrently continuously throughout thefilamentary structure.

with the polymer as a single stream, the cross section of the concurrentstream of the filament-forming liquid having an inner area and asurrounding outer area, the said inner area surrounding the extrudedpolymer and being in laminar flow and the said outer area being in astate of turbulent flow which proceeds concurrently with the polymer inthe form of a helix around the inner area of laminar flow.

The terminology process to form a filamentary structure is used todescribe the conventional processes, such as the ones hereinbeforementioned. It thus includes the conventional wet-spinning and the matrixtype of spinning procedures. The term a filamentary structure is used todesignate a structure which is long as compared to its width or crosssection, such as a filament, fiber, ribbon or the like. The term freshlyextruded is used to signify that the polymer has recently come from theextrusion orifice and that it has not as yet been completely changed toa structure in which the final polymer runs continuously throughout thestructure. The term filament-forming is used to describe a liquid whichcauses the polymer to solidify or coalesce so that it is distributed Thefilament-forming liquid may thus be either a coagulating or a coalescingliquid for in each case it causes the polymer to be continuous throughthe structure. The terms laminar flow and turbulent flow are given theirconventional meaning as in hydraulics. The term laminar flow thus meansstreamline or viscous flow whereas the term turbulent" means that theflow is non-laminar or in a state of turbulence.

The desired flow of the present invention is obtained by the use of anovel enclosure which imparts this how pattern to the filament-formingliquid. One type of enclosure for achieving this flow is a non-round orelliptical tube twisted lengthwise about its axis, the turns being inthe same or in alternately opposed directions. Such a non-circular crosssection can be given to a tube by indenting the tube, by creasing thetube, by partially flattening the tube to an oval shape, by the propermolding or extruding of the tube, etc., or by a combination of these orother operations. Each of these tubes has an inner periphery which isnon-uniform. A liquid which would normally pass through the tube inlaminar flow is thus given'an outer area of tubulence. The preferredtubes employed in this invention are those which have an oval orelliptical cross section with a maximum internal free passageway ofabout 1 inch, a length of from about 1 to about 16 feet and a twist offrom about i 1 to about 10 turns per foot.

In the accompanying drawings which illustrate preferred embodiments ofthe invention,

Figure 1 is a diagrammatical flow sheet of this invention as applied tothe matrix or dispersion type of spinning process;

' Figure 2' is. a diagrammatical flow sheet of this invention as appliedto the coagulation type of spinning process; and

Figure 3 is a plain view of one enclosure which may be used in thepractice of this invention.

In Figure 1, a dispersion of the synthetic polymer particles is preparedby polymerizing the monomer in an aqueous medium containinganemulsifying agent. This dispersion is stored in tank 1. A quantity ofan aqueous solution containing the matrix-forming material, such as aone percent by Weight solution of sodium alginate is prepared and storedin tank 2. The contents of both tanks are then mixed in a mixer 3 toform a modified dispersion. The mixture is pumped by pump 4 through afilter 5, then through the orifices of spinneret 6 into the coagulatingor setting medium 7, to form the filaments 8. The filaments comprisingthe gel matrix containing immobilized discrete particles of polymer areconverged over roll 9 and led through funnel 10 into the coalescing tube(twists not shown) 11. The coalescing liquid is fedinto trough 12through tube 13. An overflow tube 14 allows a constant head to bemaintained in trough 12. After several feet of concurrent travel throughtube 11, the coalescing liquid and filament are led into trough 15containing additional coalescing liquid. The filament then passes overthe edge of trough 15 into trough 16 which contains wash water. Afterbeing washed, the filament is led under roll 17 to the Windup 18.

In Figure 2, a solution of the polymer from supply pipe 20 is extrudedthrough spinneret 22 into a coagulating bath 29 maintained at a constanthead in tank 30 by means of an adjustable overflow 21. The extrudedpolymer proceeds through twisted tube 23 along with the coagulatingliquid 29 into trough 19, which contains additional coagulating liquid29'.- The trough 19 is equipped with an adjustableoverflow pipe 24 tocontrol the liquid level in the trough. The filament upon emerging fromthe coagulating liquid 29 in trough 19 is carried over a guide roll 25around wash rolls 26 into wash water 28 to windup 27.

Figure 3 is a detailed illustration of a section of one of the tubesused in the process of the present invention. The tube is noncircula-rin cross section and is twisted about its axis to provide a spiralpattern.

The invention is illustrated by the following examples which are citedto illustrate the invention but are not intended to limit it in anymanner. Unless otherwise stated, all percentages mentioned in thespecification are by weight. When tubes are employed in the followingexamples, the differential (hydrostatic) head: between 'the two bathsconnected by the tube is maintained at about 4 inches.

Example I is then passed over a wheel into a coalescing bath containingcalcium thiocyanate at 103 C. In this bath the filament is passedthrough a 4.5 foot straight bore smooth-walled inch internal diameterglass tube at a rate of 30 y.p.m. The filaments are washed and wound upat 33-40 y.p.m. These filaments cannot be drawn more than about 8X.Portions of these filaments drawn 7 in water heated at 100 C. have thefollowing properties:' tenacity-:43 .g.p.d., elongation =24%, andinitial modulus=35 g.p-.d.

No improvement is noted it a flexible tube is used in place of the glasstube and the filamentpassed through this tube arranged in a spiralpattern. For example, the dispersion described in the first paragraph isextruded through a 40 hole- 3 mil spinneret into a 5% calcium chloridebath, and. then passed over a wheel into a coalescing bath containing'6570% of calcium thiocya nate heated to 102 C. In this bath thefilament is passed at approximately 29 y.p.m. through 6 feet of 0.75"inch internal. diameter flexible plastic tubing arranged in the form ofa coil and then Washed. Portions of these filaments drawn 7X in waterheated at 100 C. have the following properties: tenacity=3.7 g.p.d.,elongation-=31%, and initial modulus=39 g.p-.d.

The following data show the advantage of the tube design of thisinvention. A 4.5 feet, 0.75 inch internal diameter stainless steel tubeis flattened to an oval shape and twisted approximately 3 turns/ft. A40% disperslot: (550 grams) of polyacrylonitrile is mixed with 515 gramsof a 1% sodium algina-te solution containing 0.5% of sodium laurylsulfate. Filaments are prepared hy extruding (using the apparatus ofFigure 1) at approximately 50 y.p'.m. and coagulating as described inthe-preceding two paragraphs. The coagulated gel filament is then passedover a wheel into a calcium thiocyanate solution heated at 110 C. Thecoagulated gel filament is passed along with this solution throughthe'twisted stainless steel tube where coalescence occurs. The filamentsare then washed and wound. The c0- aiiesced' filaments can be drawn asmuch as 22x. The following table shows the properties obtained atvarious draw ratios:

w r Tenacity Elonga Initial Draw Ratio (g.p. l.)- tion Modulus Denier y(percent) (g.p.d.)

Example 11 lPoh/(tetramethylene oxide) glycol (124.5 grams=0.12 mol)having a molecular weight of 1035 is reacted with 10.50 grams (0.06mol.) of 4-methyl-m-phcnylene diisocya-nate by stirring in an anhydrousatmosphere for 3 hours at. steam bath temperatures. To this dimer withhydroxyl ends is added without cooling 30.0 grams f (0.12 mol.) ofmethylene bis(4-phenylisocyanate) dis material as determined byevaporation of a portion. 7 I

into an aqueous coagulating bath containing 5% by weight of calciumchloride. The coagulated gel filament 0.32 grid. and an elongation of418%.

solved in-dry methylene chloride and the mixture allowed to react. for 1hour at steam bath temperatures. Thefdimer iwith isocyanate ends isallowed to cool and 400- grarnsof N,N-dimethylformamide added. To thissolution is added 3.0 grams (0.06 mol) of hydrazine hydrate dissolved in26 grams of N,Ndlimethyl-formamide. The resulting polymer solution,which contains approximately 28% -solids, is diluted withN,N-dimethylformamide to produce a spinning solution containing about20% solids. i

The solution is extruded throu gh a 20 mil single hole spinneret intovaryingaqueous baths heated at C. A filament formed at arate. ofapproximately 50 y.p.m. by extruding into water-is found to have atenacity of By changing the coagulationbath to one containing 50% byweight ofi N,N-dimethylformamide, filaments can be obtained from thissolution which have a tenacity of 0.56 g.p.d; and an elongation of 570%.This represents greatly improved physical properties, because thetenacity has been markedly increased with an accompanying increase inelongation. The improvement in properties is attributed to the presenceof the N,Ndimethylformamide in the spinning baths, which causes slowercoagulation and the formation of a more desirable structure.

However, despite the fact that the ultimate properties are better, thefilament initially formed when this bath is used is actually muchweaker. Consequently, in order to maintain spinning continuity, it isnecessary to reduce the spinning speed materially. Spinning continuitycan be maintained at a satisfactory level using spinning speeds of 50y.p.m. with this bath while still retaining the desirable level ofproperties (e.g., filaments with a tenacity of approximately 0.5 g.-p.d.and an elongation of approximately 600%) only by using the twisted tubeof the preceding example in the spinning bath as shown in Figure 2. Theuse of a twisted tube made of a transparent material shows that therunning filament stays in the center of the twisted tube and does notcome in contact with the Walls. Further tests show that flow contains acentral area of laminar flow (through which the filaments pass) and anouter area of turbulence adjacent the wall of the twisted tube.

Example [11 A polymer with an inherent viscosity of approximately 1.62in sulfuric acid is prepared from m-phenylene diamine and isophthaloylchloride. A portion of this polymer is dissolved inN,N-dimethylacetamide to produce a solution. containing approximately19.5% of the polymer and 4.5% by weight of calcium chloride (based onpolymer weight). This solution is heated to 60 C. and extruded through a100 hole 3 mil spinneret into a bath maintained at 60 C. which containsa mixture of 35% by weight of N,Ndimethylacetamide, 20% of calciumchloride, and 45% by weight of water. After passing throughapproximately yards of this bath at a rate of 18 yards per minute, thefilament is transferred to a bath of Water at room temperature. Afterpassing through approximately 18 yards of this bath at the same speed,the filaments are collected on a bobbin. 'The filaments are drawnapproximately 1.5 X while passing through these baths. They aresubsequently after-drawn bypassing through steam and over a hot-plate toproduce a filament which has had a total draw of approxi- I Following isa comparison of the properties of the filaments obtained by these twodifferent processes:

. Tenacity Elouga- Initial Denier (g.p.d.) tion Modulus (percent)(g.p.d.)

control; 2. 4 2.8 42 5e Tube-Spun 2. 5 4. 5 40 67 This exampledemonstrates that the use of the twisted tube results in the formationof filaments with substant-ially superior properties even when higherspinning speeds are used. The following example shows that theproperties are more divergent when equal spinning speeds are used. 1

'6 Example IV The polymer used in the preceding example is dissolved toform a solution of the same composition. The

spinning conditions are identical with those described in TenacityElonga- Initial Denier (g.p.d.) tion Modulus (percent) (g.p.d.)

Control 4. 1 1. 7 24 42 Tube 2. 2 4. 4 31 76 The use of the specialenclosure permits one to at least double, and in some cases more thanquadruple, the rate of spinning without increasing the number of breaksin the thread line. While a tube of one particular designhas beendemonstrated in the examples, any enclosure which imparts the desiredflow to the coalescing bath as it flows concurrently with the filamentscan be used. 1

Another advantage of the special enclosure, of the present invention isthe fact that string-up trouble is practically eliminated when spinningis initiated. In the prior art, when tubes were used, the freshly spunfilament was led into the tube where it often became tangled .to such anextent that the tube became partially or totally obstructed and spinninghad to be restarted. When employing the process of the presentinvention, however,

the freshly spun filament is carried through the tube with substantiallyno tangling of the filament or plugging of the tube passageway. 1

Many types of materials may be used for preparing the tubes employed inthe present invention. For example, ordinary glass and plastic tubingmay be used. The flow.characteristics in tubes of metal or plastic orglass can-be modified by pressing dimples or rings into the outsidesurface to form irregularities on the inner surface. The tube may alsobe made uneven by corrugating or sand blasting. The tubing can also bemade from elastomeric materials, which can, if desired, be distorted ormade uneven by applying an irregular outer cover prior to vulcanization,or by using an irregular curing mold.

As mentioned earlier, the process of this invention is useful whenutilized in the preparation of rubber threads from latices. The usualprocesses for preparing rubber threads in this manner are well known inthe art. Latices from natural rubber or synthetic polymer laticesprepared by emulsion polymerization may be used. The stabilizedemulsions are extruded through suitable orifices into a coagulatingbath. Acetic acid has been suggested as a suitable coagulant. Thefreshly formed thread line is very weak and very gentle handling isrequired. The process of this invention is well suited to the handlingof this thread line during its formative stages. The apparatus is alsowell suited to the processing of highly elastic filaments fromcondensation elastomers. This is a conventional wet-spinning process inwhich solutions of the elastomers are extruded into a coagulating bath.Typical condensation elastomers are those in which a low molecularweight polymer with active hydrogen ends, such as a polyester of apolyether glycol, is reacted with a diisocyanate and thisisocyanate-terminatedlow molecular weight polymer is chain-extended witha difunctional active hydrogen compound. As is true in the case of theaddition elastomers, the freshly formed filaments tend to be quite weak.These filaments increase in strength upon further treatment in the bath,but very low spinning speeds must be used until coalescence issufliciently complete to permit more rapid processing. The use of theflow of the present invention eliminates contact with the walls of thetube. This factonin conjunction with the concurrent 'bathflow madepossible by the use of this tube,'reduces the tension on the filamentsand permitsspinning speedstobe increased from approximately 30 y.p.m. toapproximately 100 y.p.m.

The process of this invention is particularly well adapted to theprocessing of the relatively weak freshly formed filaments obtained byextruding dispersions of water-insoluble synthetic linear polymers in asolution of a matrix-forming material. This process has been referred toearlier and Will be described in detail in the following'sections. Thefollowing advantageshave been observed when the process of thisinvention is applied to the preparation of filaments by thisr'riethod:'"

(:1) No dragging or snagging of'the'filaments on'the walls of the tube.e I

(2) Better coalescence of the'polyiner particles embedded in the matrix.

(3) Filaments are obtained which are more readily drawable and can bedrawn to a final lengthwhich is a much higher percentage of the originallength than is possible without the use of this tube.

(4) Yarn obtained is free of loops.

(5) Much'highe'r spinning'speeds are possible.

(6) Fewer interruptions in the spinning'process due to filamentbreakage.

(.7) Permits use of baths which would otherwise be impractical becauseof the weak thread line'de'veloped.

As illustrated by the examples, attemptsto' use a'nun modifiedcylindrical tube, or even a cylindrical tube arranged to form a spiralpassage, does not provide comparable results. The filaments tend to hangup on the Walls of the tube and breakage of the thread line results whenspeeds substantially above about 30 yards per minute are tried whenpreparing filaments from polymer dispersions. Despite the fact that theturbulence, along with the laminar flow, Within-the tube would appear torepresent a harsher treatment for the filaments, theresults-demonstrate-that thereverse is actually true. I

The preparation of filaments from polymer particles dispersed ina'solution of a matrix-'formingmaterial is a recently developed processwhich has not been described extensively in the literature. Accordingly,it 'will'be described in more detail than the other spinningprocesseswell-known in the art which maybe improved by the use of this invention.In general, the dispersion spinning process may be used to prepare filmsand fibers of waterinso'luble synthetic linear polymershaving.amolecul'ar weight of 10,000or higher. Someof the many polymers that canbe used'include: acrylonitrile polymers and copolymers; polyacrylic andpolymet-hacrylic esters, such as poly(methyl methac-rylate); poly(vinylchloride) and copolymers of vinyi chloride with vinylesters,acrylonitrile, vinylidene chioride, and the like; copolymers of vinylcompounds with conjugated dienes such as butadiene; 'vinylidene chloridepolymers; polyethylene; polytetrafluoroethylene;polychlorotrifluoroethylene; poly('viny1 acetate); partially hydrolyzedpoly.('vinyl esters) poly (methyl winyl ketone); polyvinyl ethers;chlorosulforiated polyethylene; poly(vinyl carba'zole); poly(vinylacetals) poly- Jamides, such as poly(hexamethylene adipamide),poly(N-:methoxymethylhexamethylene adipamide) polytethylene :sebacamide),polyQmethylene bis-[p-cyclohexylene] adipamide); polysulfonamides;polyureas, such'as -poly(tetramethylene urea); polyurethanes, suchasthose' prepared from piperazine; polyesters, such as, poly (e'thyleneter ephthalate), and elastic copolyesters, such asthose prepared from amixture of aromatic and aliphatic dib'asic acids and a suitable. glycolpdlyesteramidesppolytliiolesters; 'poly'sulfones; polyethers; cellulose'derivatives, such as cellulose acetate, and many others. Copolyrners ofall types can be used as wel-l as' the vhor'ntzrpoflyiners listed;

The term copolyrner is intended-"to include an types, such 'as random,alternating, segmented or block, and graft oopolymers. The polymerparticles may even be cross linked, providing the degree or tightness oforess linkin'g is not suflicient to prevent the coalescence required toproduce the desired structure. a

The matrix-forming materials useful in the invention comprise cationicor anionic polymeric electrolytes or neutral or non-ionic polymericmaterials which are soluble in the dispersion ofthe fiber-formingpolymer and which can be shaped in aqueous or non-aqueous media.Suitable anionic polymer materials contain a plurality of acidic groups,such as carboxyl, su1fonic and/erphosphoric or other acid groups.Specific polymers and classes of polymers Whichare applicable -asanionic matrix-forming materials iii this process include the following:alginates, carboxyalkylcelluloses,carb'oxy'rnethylhydroxyethylcellulose's, viscose, polyacrylates,'polymethacrylates, and the like. In most cases the monovalent alkalimetal salts of the anionicpolymeric electrolytes are more soluble inWater and are preferred.

Cationicpoly'meric electrolytes suitable as matrix-forming materialscoritain'a plurality of basic groups. These are usually amino and/ orquaternary ammonium groups. Examples of useful cationic polymericelectrolytes are polyvinylpyridine, diethylamin'omethyl methacrylatepolymer, hydrolyzed copolymers of vinyl acetate and vinyl pyridine,N-yinylphthalimide, N vinylsuccinimide, and other vinyl-substitutedamino and masked amino polymers.

- Neutral polymers which may he used as matrix-forming materials includemethylcellulo'se, hydroxyethylcellulose, cellulose acetate,urea-formaldehyde and melamine-formaldehyde resins, cyanoethylcellulose,poly(vinyl alcohol) and polyacrylamide.

Only small amounts of matrix-forming material are required to provide adefinite advantage over 'none at all. The quantity used ranges from0:10% to 10% by weight of the dispersion, with'0.25' to 5% beingpreferred. The specific quantity preferred varies with'the matrixmaterial.

The setting or immobilizing medium maybe any liquid or vapor capable ofprecipitating or gelling the matriX- forming material. This includes airand vapors such as volatile strong acids, e.g., hydrogen chloride. Alsouseful are various other compounds and/ or mixtures in liquid or vaporform, such as water miscible organic compounds and aqueous solutions ofsolid, liquid, or gaseous inorganic and/or organic compounds.Preferably, aqueous solutions are used'which contain alowconcentrationteg, O.540% by weight of. the aqueous solution) of anelectrolyte or a non-electrolyte. Typi'cal' useful non-eleet'rolytes arewater-miscible'org'anio liquids, such as alcohols, ketones, or glycols.High or low temperatures maybe used in coagulating baths to develop thedesired precipitating qualities of the particular setting agent beingused.

When aqucousbaths are used, the anionic and cationic matrix-formingmaterials will generally be terms into shaped articles through 'gelationas a result of chemical action on the materials hy the coagulating bath.Aqueous solutions of polyvalent'i'iietal salts are particularly usefulas precipitants when an anionic matrix-forming material is used. Whenaneutral, water-soluble polymeric material is used, physical gellingaction of the coagulating 7 bath will most likely be involved.

The choice of matrix-forming material depends to some extent on thewater-insoluble dispersed polymer. 7 It 'is' Water-soluble salts arepreferred as coalescing solutions and include preferably metal salts ofinorganic acids. These salts should be sufiiciently soluble in water toyield 10% solutions and, preferably 30% solutions. Furthermore,concentrated aqueous solutions of the salt being used should be capableof dissolving the polymer being processed at. some temperature up to theboiling point of the salt solution, for example, from C. to 175 C., andgenerally from 20 C. to 120 C. Coalescence can also be achieved by theuse of organic coalescing agents. Organic compounds which are to be usedshould, preferably, be capable of dissolving the polymers at atemperature below their boiling points. However, temperatures higherthan the boiling point of the liquid may be used for conducting theprocess in the vapor phase or under pressure. In practice, anycoalescing agent need only exert a solvent action on the polymer thatcan be regulated to achieve the desired fusing of the discrete polymerparticles.

It is possible to extrude the polymer dispersion into a liquid mediumwhich will precipitate the matrix-forming material and will also exertsolvent action on the polymer particles in the precipitated matrix. Inthis case, the special enclosure would be used in the single bath systemto protect the filaments during the combined coagulation andcoalescence.

In coalescing the polymer particles room temperatures or lower can beused, but it is generally preferred that the coalescing bath be heated,since less time is needed. For example, temperatures of the order of30-175 C. may be employed momentarily in transforming the semirigidshaped article to a transparent, coherent film or fiber. Low timeconsumption is preferred in continuous processes and it is advantageousthat the coalescence step consume only a few seconds or less. The use ofthe flow pattern of this invention is particularly useful in this stepof the dispersion spinning process.

Removal of the coalescing agent from the shaped polymer is readilyaccomplished by washing. In washing multifilaments it is generallypreferred that cold water be used. The resulting structure may then beaftertreated with boiling water, and, if desired, stretched to orientthe molecules to effect improvement in physical properties. On the otherhand, the coalesced structure may be atleast partially oriented bydrawing prior to the washing step.

In addition to water, matrix-forming material, and polymer, thedispersion used for producing this shaped article can contain dispersingagents, plasticizers, pigments, non-solvent salts, dyes, clay, silica,alcohol, acetone, and similar materials. Alternatively, these materialsmay be incorporated in the coagulating bath, in the coalescing bath, orin separate baths or combinations thereof. These substances may or maynot appear in the shaped article. If desired, the coagulated articlesmay be passed through a bath between the coagulating and coalescingmedia for washing, filling, plasticization,

and the like, prior to coalescing. After coalescing, the.

shaped article may be treated with a suitable finishing agent to enhanceits usefulness or to facilitate subsequent processing.

The filaments which are produced in accordance with the presentinvention are useful in filter cloths, conventional textile fabrics,industrial fabrics, elastomeric fabrics and the like.

Many modifications will be apparent to those skilled in the art from thereading of the above without a departure from the inventive concept.

What isclaimed is:

1. In a process of forming a filamentary structure by contacting afreshly extruded polymer with a filamentforming liquid to form afilamentary structure; the improvement which comprises flowing thefilament-forming liquid concurrently with the polymer as a singlestream, the cross section of the concurrent stream of thefilamentforrning liquid having an inner area and a surrounding outerarea, the said inner area surrounding the extruded polymer and being inlaminar flow and the said outer area being in a state of turbulent fiowwhich proceeds concurrently with the polymer in the form of a helixaround the inner area of laminar flow.

2. In a process of forming a filamentary structure by contacting afreshly extruded polymer, the said polymer being present as particleswhich are immobilized in a gel matrix, with a coalescing liquid tocoalesce the polymer particles into a filamentary structure; theimprovement which comprises flowing the coalescing liquid concurrentlywith the polymer as a single stream, the cross section of the concurrentstream of the coalescing liquid having an inner area and a surroundingouter area, the said innerarea surrounding the extruded polymer andbeing in laminar flow and the said outer area being in a state ofturbulent flow which proceeds concurrently with the polymer in the formof a helix around the inner area of laminar flow.

3. In a process of forming a filamentary structure by contacting afreshly extruded polymer solution with a coagulating liquid to coagulatethe polymer into a filamentary structure; the improvement whichcomprises flowing the coagulating liquid concurrently with the polymeras a single stream, the cross section of the concurrent stream of thecoagulating liquid having an inner area and a surrounding outer area,the said inner area surrounding the extruded polymer and being inlaminar flow and the said outer area being in a state of turbulent flowwhich proceeds concurrently with the polymer in the form of a helixaround the inner area of laminar flow.

References Cited in the file of this patent UNITED STATES PATENTS827,434 Friedrich July 31, 1906 1,619,768 Schubert Mar. 1, 19272,402,846 Ryan June 25, 1946 FOREIGN PATENTS 293,977 Great Britain July19, 1928 UNITED STATES PATENT OFFICE CERTIFICATE OF "CORRECTION PatentNo, 2., 955 o17 October 4 1960 I Clarence Boyer- Q It is herebycertified that error appears in the printed specification of the abovenumbered patent requiri ng correction and that the said Letters Patentshould read as corrected belo Column 4 lines 64 and 65 forN,N-dimethyl-for'mamide" read N N-dimethylformamide column 6 line 67 4for "of" read or Signed and sealed this 11th day of April 1961,

(SE/AL) Attest: ERNEST w. syvmER a v ARTHUR W. CROCKER Attesting OfficerActing Commissioner of Patents

1. IN A PROCESS OF FORMING A FILAMENTARY STRUCTURE BY CONTACTING A FRESLY EXTRUDED POLYMER WITH A FILAMENTFORMING TO FORM A FILAMENTARY STRUCTURE, THE IMPROVEMENT WHICH COMPRISES FLOWING THE FILAMENT-FORMING LIQUID CONCURRENTLY WITH THE POLYMER AS A SINGLE STREAM, THE CROSS SECTION OF THE CONCURRENT STREAM OF THE FILAMENTFORMING LIQUID HAVING AN INNER AREA AND A SURROUNDING 